Guest Post by Willis Eschenbach
Of late there has been a lot written about the effect of “black carbon”, a.k.a. “soot”, and also “brown carbon”, a.k.a. wood and dung smoke, on the climate. Me, I think it’s worthwhile controlling black and brown carbon solely because of the health effects. Inhaled soot and wood smoke kill a lot of people every year. So reducing atmospheric black and brown carbon is an example of the “no-regrets” actions I have been advising that we should take. It is of value whether or not black carbon affects global climate.
And city dwellers are familiar with the phenomenon that when soot falls on snow, it absorbs sunlight, warms, and speeds the melting of the snow. In the country, people spread firewood ashes on frozen walkways to melt the ice. So black carbon tends to melt snow and ice, and thus reduce snow and ice albedo, and thus warms the climate. How much? Unknown, but estimates say black carbon is a definite factor in the Arctic warming.
However, there is one major misconception out there about the effect of black carbon on climate. It shows up in a recent editorial by Richard Kerr in Science magazine.
A Quick (Partial) Fix for an Ailing Atmosphere
Science 13 January 2012: , Vol. 335 no. 6065 p. 156 , DOI: 10.1126/science.335.6065.156
The world’s air could use a quick scrubbing. So a group of scientists has come up with 14 practicable approaches to doing just that. The researchers say the selected cleaning methods, described on page 183, would more than pay for themselves in lives saved and crop yields increased while cutting global warming to boot. “Technically, it can be done,” says atmospheric scientist Mark Jacobson of Stanford University in Palo Alto, California, who was not involved in the work. “It’s a question of will power.”
Scientists and policymakers alike have long known how, in principle, to get a quick start on cleaning up the atmosphere: Stop the gush of short-lived pollutants. Carbon dioxide will remain in the atmosphere for centuries, warming the world all the while, but pollutants like soot and methane remain airborne just a few weeks and a decade or so, respectively. Stop their emissions and their concentrations would promptly start dropping, sharply.
And that would be a good thing. Inhaled soot, also called black carbon, kills or debilitates millions of people each year, while soot in the atmosphere tends to warm climate, mainly by absorbing more sunlight.
It is the last statement, “soot in the atmosphere tends to warm climate, mainly by absorbing more sunlight”, that is in error. I can show this by means of a curious thought experiment, by taking black carbon to extremes.
The logic of their claim goes like this. The earth receives a global 24/7 average of 342 W/m2 at the top of the atmosphere. Of this, about 107 W/m2 is reflected back into space. Black carbon is very much like an ideal blackbody, it absorbs just about all of the light that hits it. The claim is that black carbon in the atmosphere absorbs the incoming solar radiation, so it cannot be reflected back to space. In addition, it also absorbs sunlight reflected from the ground and prevents it from escaping to space. So it intercepts and absorbs sunlight in both directions.
As a result, the system has to end up warmer than it is at present.
And to be fair, that all sounds eminently logical. We end up with more energy in the system, the atmosphere ends up warmer, because the black carbon is absorbing both more sunlight and more reflected sunlight. “Simple physics”, as the AGW folks are fond of saying.
So, here is the thought experiment. Suppose we have a planet just like the Earth, that receives a global 24/7 average of 342 W/m2 at the top of the atmosphere and reflects about 107 W/m2 back into space
We start adding black carbon to the atmosphere. We note that as Richard Kerr says, the black carbon absorbs more and more of both incoming (solar) and outgoing (reflected solar) radiation. Just as their logic says, there’s less and less energy reflected back into space.
We add more and more black carbon, slowly absorbing more and more sunlight and reflecting less and less sunlight. Finally we have added so much black carbon that it forms a shell of solid black carbon entirely surrounding the planet, say 20 kilometres above the surface. This shell is not reflecting anything at all, it is absorbing all the sunlight.
What happens to the temperature of the planet? This is the extreme case of black carbon in the atmosphere, and so it will tell us what the net effect is of adding black carbon to the atmosphere.
Well, we know that the shell has to radiate the same amount of energy that it receives, both inwards and outwards. Since the shell is the only thing heating the planet, that means the planet must be at the same temperature as the shell.
And what temperature would that be? Well, it would be the blackbody temperature sufficient to radiate 342 W/m2, which is … wait for it …
5.5°C or 42°F
This is well below the current temperature of the planet, which is usually taken to be about 14-15°C, or 58°F.
And this means that black carbon in the atmosphere cools the planet.
So where did the logic go wrong?
Their logic went wrong by not considering the effect of atmospheric black carbon on the poorly named planetary “greenhouse effect”. The greenhouse effect works because sunlight strikes the surface. When that energy is radiated back out towards space, some of the energy is absorbed by the atmosphere.
About half of that energy is radiated from the atmosphere back to earth, while the rest is radiated back to space. As a result, the earth ends up warmer than it would be without “greenhouse” gases in the atmosphere.
But when atmospheric black carbon absorbs the solar energy, only about half of the absorbed energy is radiated down to the surface, with the rest radiating upwards towards space.
And as a result, the surface only receives half the radiant energy from the sun that it would have gotten if the black carbon were not there.
In other words, atmospheric absorption of solar energy by any aerosols or molecules, including black carbon, reduces the efficiency of the greenhouse effect. Instead of the surface receiving energy from both the sun and the atmosphere, when black carbon intercepts the sunlight, the surface receives energy solely from the atmosphere.
For the greenhouse effect to work, the sun has to strike the surface. Any solar absorption in the atmosphere reduces the greenhouse effect, and in the extreme, total solar absorption in the atmosphere reduces the greenhouse effect to zero.
And as a result, as the thought experiment shows, adding black carbon (or anything that absorbs sunlight) to the atmosphere cools the planetary surface.
I cannot let this go by without expressing my displeasure at the use of bad science in pushing public policy. As Richard Kerr has just amply demonstrated, the understanding of climate even among scientists is still far too poor to serve as a base for any kind of policy decisions.
w.
Markus Fitzhenry” CO2″‘
I don’t talk about CO2 but carbon black(particles)
Willis: excellent point. It’s easy to get caught up with simplifications like “imagine a spherical cow in space”, which have no practical meaning. But I think you do need to listen to folks like David J. Ameling, above, who make the point that it depends on how high in the atmosphere your soot is. You say that soot on the ground is quite different than soot in the atmosphere, but it’s really only a matter of degrees. Your thought experiment could be: imagine the surface of the earth coated with soot, then imagine that layer of soot was floating 3 feet in the air, then 300 feet, 3,000 feet, …, 12,000 miles, …
It seems reasonable that the higher the absorbing layer, the more direct the path to space for the blocked-and-upward-radiated energy.
Heh. I always wonder what word-induced image is in the mind of someone who writes “peaked interest” instead of “piqued interest”. A peak, after all, is a tall maximum, beyond which comes a fall-off. So do they mean “reached a temporary ceiling”? Or just that it was spiked.
IAC, piqued means stimulated, no geometry involved. (In this context. In others, it can mean irritated. Of course, in biology and medicine, irritate means stimulate! So that’s OK. 😉 )
Well, well, well …. this is essentially what I have been saying for the last year. Black carbon is nothing more than a big GHG. Or, if you prefer, CO2 and other GHGs are just little pieces of black carbon.
I’ve been stating time and again the these radiating entities have BOTH a warming and cooling effect. The climate crowd focuses on the warming effect and ignores the cooling effect. The key has to do with being well mixed in the atmosphere. When this is the case the warming and cooling effects balance out and we end up with a lapse rate that is dependent, not on the concentration of these elements, but on the physical structure of the atmosphere. This is the effect noticed by K&Z and others who have tried to claim that gravity is responsible for the GHE.
Due to the balance of the warming and cooling effects it does not matter if more GHGs are added to the atmosphere as long as they are well mixed. Of course, there are times when the mixing is not perfect. One of these is large volcanoes injecting particles high in the atmosphere (and thus enhancing the cooling effect). Another is very humid (or very dry) regional variations. However, overall that stuff averages out over time and our global temperature varies within a few degrees.
Wayne2 says:
February 8, 2012 at 6:33 am
Willis: excellent point. It’s easy to get caught up with simplifications like “imagine a spherical cow in space”, which have no practical meaning. But I think you do need to listen to folks like David J. Ameling, above, who make the point that it depends on how high in the atmosphere your soot is. You say that soot on the ground is quite different than soot in the atmosphere, but it’s really only a matter of degrees. Your thought experiment could be: imagine the surface of the earth coated with soot, then imagine that layer of soot was floating 3 feet in the air, then 300 feet, 3,000 feet, …, 12,000 miles, …
It seems reasonable that the higher the absorbing layer, the more direct the path to space for the blocked-and-upward-radiated energy.
Yes, yes, yes … my point exactly. Now, consider that in reality the turbulence of the atmosphere causes a distribution that has no layer at all. Instead, some of the particles at low altitudes do warming while other particles at high altitudes do cooling. So, when additional particles are added to the atmosphere they mix over time and the total effect balances out.
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Paul Kelly says:
February 8, 2012 at 5:01 am
The implication is that the effect of black carbon depends on the height of the carbon in the atmosphere. My guess is that the average height is closer to one meter than to 20 kilometers, so the net effect is warming.
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Yes, it depends on where the BC is. If it’s low in the atmosphere or on the ground, that’s where warming occurs (assuming its presence reduces the albedo). Further up, I’m not certain (the extreme case of a BC shell well above the surface would definitely cool the surface because sunlight would be completely blocked & you might end up w/a negative lapse rate?), but generally I’d agree that most of the BC stays fairly close to or even on the ground (look at the buildings in some European cities).
I highly doubt that soot, dirt, and carbon black alone could melt significant portions of the Arctic or any other large snow mass. Have you ever seen a major city like Chicago in the winter? Once it snows, the snow can stay for up to four and sometimes six months. All the while getting ugly and becoming an eye sore until there is enough sun light and the ambient air temp gets warm enough to melt it. This can be seen even in sunny cities like Denver where mountains of snow are cleared from parking lots. It takes a week or more of 40+ temps to completely melt these mountains of snow which are caked/laced with debris from the parking lot. Not to mention, these mountains of snow are sitting on one of the biggest sources of carbon black, asphalt.
/Rant…
Willis — An interesting thought experiment, as ususal, but I don’t think it works:
If there is a shell of black carbon 20 km up that is impenetrable to radiation, and its temperature is 5.5 dC, the adiabatic lapse rate below will make the surface very toasty. I basically agree with Leonard Weinstein above (2/8, 5:32 AM).
I admit I don’t understand the mechanisms that make temperatures go back up above the tropopause, but apparently they are all radiative, so that this hypothetical shell would cancel them out below itself.
It was mentioned above that volcanic eruptions tend to cool the planet. However, I believe this effect is due to high albedo SO2 and ash, rather than from low-albedo soot, so that contradicts, rather than confirms, Willis’s contention.
So I buy that soot warms the planet whether it’s on the ground or in the air. But unlike CO2, which may ward off or at least delay the catastrophic next ice age if it some of it lingers in the air, soot is only transitory and so will not have this beneficial side effect.
CO2 has been growing very stubbornly since 1958, so that the power of the biosphere and hydro/lithosphere to reabsorb it as kudzu or plankton shells appears to be limited. Two recent articles by Dana Royer argue that over the past 550 million (not thousand) years, glaciation is always associated with CO2 under 500 ppm, so that could be a very desirable level to strive for.
All policy makers need is the impression of good science.
No one would care if life changing policy making (law and regulation) were not at stake here and if it impacted no one other than the policy makers and global warming scientists but they intend to drag the entire population into their scheme.
The global warming crowd are like Don Quixote a knight ‘Tilting at windmills’ for no logical reason except in his own mind and self-interest and not taking into account he was attacking private property, others income and free enterprise.
Perhaps no one told them as children that honesty is the best policy.
There is another adage waste not want not and that goes for good science as well.
Markus Fitzhenry:
Could you give me an English translation of this paragraph? Seriously, what is a “latent force” and what is the question that you are even asking?
Given how little understanding Bob has shown regarding convection over in this thread: http://wattsupwiththat.com/2012/02/03/monckton-responds-to-skeptical-science/ , it must be a most illuminating discussion, as seems to be true of most discussions over at tallbloke’s blog. (And, by the way, unlike Willis I am not as wedded to the principle of not increasing tallbloke’s views, so I do look at things over there just for entertainment value even though I am banned from posting there, as it seems are many people who might endanger the discussions there by injecting actual science into them.)
The misunderstanding is the assumption that the W/m2 received and emitted is everywhere the same.
This is not the case. At the equatorial region W/m2received = W/m2emitted + Q
Polar region W/m2received + Q = W/m2 emitted
Q represents the lapse rate (by lattitude) from equatorial region to the polar region.
Now you get four cases.
1. No carbon black in the atmosphere or on the ground T avg = 15 oC and the dT(eq/pol) is at maximum, lapse rate Q(1)
2. Assume carbon black in the atmosphere(not on ground) only in the equatorial region (cooling) Tavg < 15 oC lapse rate Q(2)
I have found that when I add E+T to AH the humidity at AH and temperature rise’s. E=energy, T=teapot, and AH =Atmosphere inside Home.
However when I add external wind factor (hot or cold) via my Swamp cooler (The Ocean) the humidity and temperature drops to an agreable level and I sit down and have a drink.
In the winter I don’t turn the water on as that’s a waste of water. In the summer I use both water and electricity. In the winter I also collect ‘brown soot’ as my cooler is directly below my smoke stack. But I’m good there as I take my water from a shallow well and the electricity is produced by hydro dams in our local area. Plus I open my windows to get all that crap back out to the open atmosphere.
Therefore I’m good as I’m a slight shade of green, maybe limegreen.
Why is it that with all the calculations of earth’s temperature, no thought is spent on the several thousand degrees celsius core nor that just one kilometer down it is some 35°C. What I’m wondering is why not fluctuations in the core temperature eventually are felt, so to speak, on the surface? After all, those 35°C/Km for our first kilometer down is, apparently, not very static, so if that fluctuates with a couple of degrees up and down wouldn’t the surface temperature follow suite?
How does that carbon heat shield at 20 km height have enough energy to heat the surface?
Willis, as a non-scientist (I do not have a science degree) I agree with your comment that it is a good thing to clean up carbon particles which is the cause of pollution in the atmosphere. You are spot on with the comment. Again, I use observation, and in this case it is more personal because the smoke from wood fires cause asthma attacks in sensitive individuals…. yes, that is through observation!!
Also, thanks for the explanation regarding what is wrong with the more general theory regarding carbon in the atmosphere. It is all beginning to click and make sense.
“Joel Shore says:
February 8, 2012 at 8:11 am”
I’ve seen you answer, son. Sorry you can’t understand me, no I’m not. Now just close your eyes and it won’t happen.
The reason you can’t go there and play is because last time you acted like a bully, and ended up getting a intellectual beat up. And you’re in for another one.
jjmgommers says:
February 8, 2012 at 8:39 am
Gibberish.
Markus Fitzhenry. says:
February 8, 2012 at 5:44 am
“Matthew W. says:
February 8, 2012 at 4:57 am
I’m still shocked/amazed that in places like China, coal is still used as fuel for cooking at home”.
Oh come on Mathew W., how much walkabout have you done in China. I remember more cold than warm, even through the mist, morning coal stoves most corners, most towns, municipal coal powered electrical distribution along inefficient infrastructure. Street cluttered with antiqued taxis and buses. They’ve been doing it for years too.
You’ll end up with phobias, like the next bloke, if you really believe co2 adds heat to the Earth from a cooler upper atmosphere.
==========================================================
WOW !!!!!!!
“I’m still shocked/amazed that in places like China, coal is still used as fuel for cooking at home”.
I have no idea how you misinterpreted what I said.
I suggest switching to decaf
Won’t BC function as condensation cores, and thus effectively increase rather then decrease the albedo of earth?
Alexander Feht says:
February 8, 2012 at 12:21 am
Alexander, I don’t insult anyone who comes here to talk science and to contribute or learn or both. Nor have I censored anyone, as you claim.
I do not, however, suffer fools gladly, and I’m happy to speak truth to people that show up just to insult me.
If you don’t like that, I’d advise you to go be a foolish jerk somewheres else. Standing around whining because your precious feelings are hurt won’t get you any traction here.
w.
PS—So you don’t have to look it up, his footnote was as follows, along with my reply:
@Markus Fitzhenry
“How can co2 turn it’s back on incoming but catch the outgoing? Hansen mystics at work, no doubt.”
Incoming is visible light. Outgoing is IR. No mystics, nothing to do with Hansen either. The way you seem to think thermodynamics work refrigerators can’t exist.
Stephen Richards says:
February 8, 2012 at 1:06 am
it’s the unmistakeable sign of a good post …
w.
Matthew W. says:
February 8, 2012 at 11:51 am
“”I suggest switching to decaf.””
Oh come on Mathew W. only a uber-enviromentalist would equate anything with decaf. How limp wristed can you get. What you favourite cuppa? Skinny milk, soy, decaf, sugarine, latte.
John Marshall says:
February 8, 2012 at 2:51 am
Now all you need to do is to learn to distinguish between a flow of heat and a flow of energy, and you will have almost caught up with reality.
Energy can flow from cold to hot. Heat cannot.
See my post “The Steel Greenhouse” for more info.
w.
Jan Kjetil Andersen says:
February 8, 2012 at 3:14 am
No, I haven’t forgotten that, Jan. It doesn’t happen. If the planet is warmer than the shell it will lose energy to the shell until they are in thermal equilibrium. The same will happen if it is cooler than the shell, it will warm until equilibrium.
Think about it some more. With no heating, the atmosphere will be isothermal. We just went through that here, with this exact example.
w.
PS—You’ll come out looking better if you ask questions rather than make statements that are foolishly incorrect.
@David J. Ameling
High altitude black particulates capture the heat and radiate it into space before conduction and convection can tranfer the heat to the atmosphere. Low altitude black particulates capture the heat and transfer the heat to the atmosphere by conduction and convection better than the heat captured by the earths surface. This causes warming.
+++++
What happens at night? The heat capture in the daytime and efficiency of radiation on the sunny side is not balanced by the conditions at night. The ‘average insolation’ is not appropriate here. The reason is that BC is uniquely able to pick up all frequencies but kick out IR very well, as well. This is not usually the case with gases. Any global dimming from airborne BC is heating the air and in effect, reflecting energy (because it emits so well). On the other hand, BC particles below 0.1 micrometers do not scatter light. Can they radiate in IR if they cannot pick it up? I will ask my FTIR guy about that.
That aside, does the difference in the working temperature (day/night) work in favour of net heating or net cooling? At night, BC above 0.1 microns can collect collisional energy from the atmosphere and radiate it in the IR. It is literally a radiator.